In many simulation applications one of the important factors impacting through-put processing time is the need to frequently compute coordinate conversions. This is particularly important in federations including constructive simulations, simulators, and live entities (e.g. vehicles and aircraft). Such federations require methods for informing all computational nodes in the federation of information such as the time, position, velocity, and acceleration state of every entity involved. This information is contained in an entity-state protocol-data-unit (“PDU”). Informing every node in a simulation system, such as a federation of interactive simulations, of instantaneous changes in every entity-state can saturate the communication system used for interchanging such information.
In dead-reckoning methods of the prior art, all entities in the system are assumed to move in accordance with a simple kinematics model, usually in a straight line in some common coordinate system. In this manner, nodes in a simulation system can quickly compute an approximate position for an entity over a time period without having to receive more precise or exact positions from the node responsible for keeping track of or computing the more precise or exact position of an entity (the “owning” node). When an entity maneuvers in such a way to significantly depart from the simple kinematics model the nodes in the system other than the owning node (i.e., the “non-owning” nodes) will have an insufficiently-accurate approximation of the entity's position so a new entity-state is sent by the owning node to all non-owning nodes. Each non-owning node receiving the new entity-state then re-initializes the entity's simple kinematics (or kinetics) model on the receiving node. In this way, all nodes in the system have the same dynamics model for each entity and a common basis for determining position, velocity, and acceleration for each entity. When an entity maneuver triggers the issuance of a new entity-state by the owning node, the entity is said to have exceeded its dead-reckoning bounds.
In the case of federations employing the Distributed Interactive Simulation (“DIS”) IEEE Protocol Standard 1278, the common coordinate system (“CS”) of the federation is the geocentric system based on the WGS 84 ellipsoid. An individual federation node can operate in any appropriate internal coordinate system. However, the node converts information to match the DIS protocol when communicating the information to another node in the federation by sending a PDU. In such a case, the computational node (or owning node) converts entity-state data to the geocentric system prior to communicating the converted data to non-owning nodes. Conversely, when a non-owning node receives data from an owning node, the received data will be in geocentric coordinates and is converted to the internal coordinate system employed by the receiving (i.e., non-owning) node. If there are many maneuvering entities in the simulation system the networking system may become saturated with PDUs and significant latencies may occur. Additionally, the computer time needed to perform the conversions both to and from the geocentric coordinate system is a significant contributor to the latency problem.
The requirement to frequently perform coordinate conversions has a significant impact on the computer processing time within each node. It is important to use the most efficient conversion methods available. However, at the same time the accuracy of the conversion should be at a level that does not negatively impact the overall validity of the simulation.